The present invention relates to a shutter for a single lens reflex camera for measuring the luminance of an object through the camera lens with the shutter opening being temporarily opened and, more particularly, to a shutter for effecting an exposure by actuating the shutter blade by the action of a drive motor.
A shutter for a single lens reflex camera according to the prior art is described, for example, in the specification of the Japanese Patent Application No. 62-202162 of the same applicant.
The shutter for the single lens reflex camera according to this application measures the luminance of an object through the camera lens with its opening being temporarily opened and then once closes the shutter opening in response to a releasing operation to retract the mirror and the shielding plane to a photographic position. After this, the shutter blade is opened and closed to effect the exposure, and a series of operations are ended again with the shutter opening being opened after the mirror and the shielding plate are restored their initial positions.
In this shutter for the single lens reflex camera of the prior art, however, the actuating member for actuating the shutter blade to open or close the shutter opening is always biased by a spring in a direction to close the shutter blade. At the same time, in order that the shutter opening may be kept open at the start and end of the shutter, a retaining member retains the actuating member to prevent the shutter blade from being closed. As a result, the camera may have its retaining member accidently released, if an impact is applied to the camera, by the shock of the impact. In this case, there arises a problem that a photometric result becomes erroneous to make the proper exposure impossible.
Moreover, the retaining member for blocking the actuation of the actuating member in the closing direction is required for holding the shutter blade in the open position, and the use of such a retaining member is disadvantageous in that the number of parts is increased.